In spur gear planetary gearings of the conventional type, an even load distribution on the three or more planetary gears is a condition for satisfactory operating results. Manufacturing errors like true-running deviations and eccentricity of the tooth system and axial dislocations and angular deviations lead otherwise to an uneven load distribution on the individual tooth systems, which causes not only undesired noises, but in particular the lifetime of the gears and their bearings are also noticeably shortened. Many suggestions have already been made for devices, with which these errors can be balanced out and an even load distribution can be achieved.
Thus it is, for example, known to make the internally toothed ring or internal gear in two parts, wherein an internally toothed ring is surrounded concentrically by a ring which is received in the housing and a connection of the two rings occurs in the area of their separating joint through sleeve springs which are placed in coaxial grooves. In order to prevent a friction corrosion which is caused in the joints by micromovements and a quick wear of the sleeve springs, which wear is associated with these movements, here expensive measures must be taken for an oil supply into the joint. According to a different suggestion (German AS No. 1 180 210), the ring or internal gear is supported through a narrow annular surface on a relatively thin hollow-cylindrical housing wall, the free cylinder surface of which is larger than the width of the tooth. These devices bring satisfactory results for the load balance, if--what is actually the usual case--there occurs only one torque transmission in the gear box. As soon, however, as the housing is exposed to bending forces which act from outside, these forces are transmitted onto the ring gear, which again causes interference in the tooth engagement with overloading of individual areas thereon.
It is known from German OS No. 20 57 312 to form the ring or internal gear of two concentric rings which have a radial spacing therebetween, of which the inner one carries the tooth system and the outer one is connected to the housing and which are connected through a rubber ring which is vulcanized into the radial spacing gap. In place of the vulcanized ring spacer, it is possible, according to German AS No. 26 48 151, for an elastic band which is inserted between concentric tooth systems of the two rings to take over the connection. Due to the limited loadability of the rubber, these constructions are limited in their use.
It is also known to connect the ring or internal gear through a lateral, thin-wall pipelike extension fixedly to the housing (German OS No. 1 450 775), wherein said pipelike part permits in a limited degree an elastic deflection of the internal gear. According to German OS No. 21 10 252, it is also possible for the ring or internal gear to be jointedly suspended within the housing through a sleeve which is similar to a toothed coupling. While in the first case the large structural length of the pipelike extension does not permit its use for many cases, the second solution cannot be used everywhere because of the increased manufacturing expense due to each two additional internal and external tooth systems.
Therefore, the basic purpose of the invention is to produce a planetary gearing arrangement with a load balance, which is capable of both balancing manufacture-caused deviations and also keeping bending forces which act from outside onto the housing extensively away from the tooth system. The gearing arrangement does thereby not have any parts which enlarge the dimensions which are pregiven by the tooth system and the support, it is easy and inexpensive to manufacture and does not have any additional wear parts.
The purpose is attained by providing a planetary gearing arrangement, the internally toothed ring or internal gear of which can be elastically deformed in itself, wherein the deformability is approximately equal to the radial elasticity of its tooth system (mean value during the engagement).
With this it is achieved that outside influences have no or only small effects on the tooth system, on the other hand the tooth system remains sufficiently elastic in order to assure an even load distribution on the three or more planetary gears.
The invention also includes the provision of a simple construction for the internally toothed, one-piece-designed internal gear. An inner, toothed ring is connected through an annular web to an outer ring which is mounted in the gear box housing. Both rings are thereby elastically deformable under a load, without thereby substantially deforming the respective other ring, wherein the possible deformation as a whole can be determined by calculation or tests so that it corresponds approximately to the radial elasticity of the tooth system (mean value during the engagement).
The elastic deformability of the outer ring is achieved in a simple manner by an annular recess, which extends over an important part of its length.
The elastic deformability of the internally toothed internal gear in itself or its stiffness is defined, as mentioned, through the radial elasticity of the tooth system. This requirement can be met through calculations according to the finite-element-method or through tests with various designs. Thus it is for example also possible to design the web elastically deformable. Corresponding with the respectively existing loads, the internal gear can be designed as such symmetrically or asymmetrically.